Weird error while attempting to break RFC447

[arielb1]

trait Foo {
    type Out : ?Sized;
}
impl<T:?Sized> Foo for T {
    type Out = T;
}

trait Bar<T:?Sized> {}

impl<T:?Sized> Bar<<T as Foo>::Out> for () {
}
fn main() {
    println!("Hello, world!");
}

Error:

<anon>:10:1: 11:2 error: type annotations required: cannot resolve `<_ as Foo>::Out == T` [E0284]
<anon>:10 impl<T:?Sized> Bar<<T as Foo>::Out> for () {
<anon>:11 }
<anon>:10:1: 11:2 note: required by `Bar`
<anon>:10 impl<T:?Sized> Bar<<T as Foo>::Out> for () {
<anon>:11 }
error: aborting due to previous error
playpen: application terminated with error code 101

I would have expected an RFC447 error.

[arielb1]

Fixed (duplicate #26275).